It is worth noting that the chemical composition of the ICM/IGrM must therefore be markedly different than that of the stars in the BCG/BGG: as shown by [1]}, [2]}, massive early-type galaxies (ETGs) with a velocity dispersion above 200 km/s typically have high \(\alpha \) /Fe ratios up to twice the Solar value, which is inconsistent with the abundance pattern of the hot diffuse gas in their immediate vicinity (see Fig. REF ). High values of \(\alpha \) /Fe are usually associated with a very short starburst: BCG/BGGs may have made most of their stars before SNIa had time to explode, so that very few Fe-group elements are incorporated into the stars themselves. Nearly all SNIa later polluted the central ICM/IGrM instead, gradually lowering its \(\alpha \) /Fe ratios.
